Sub-miniature electromechanical medical implants with integrated hermetic  feedthroughs

ABSTRACT

Highly miniaturized electro-mechanical medical implants for certain applications cannot be fit into the available anatomic space unless their diameter can be made small enough. With devices such as rotary blood pumps or linear actuators, using rotary or linear electric motors, a thin motor stator that provides sufficient power must be encased in a corrosion resistant hermetically sealed enclosure into which electric wires must pass. Hermetic feedthroughs of the prior art are not structurally suited to maximal miniaturization with optimal electrical properties because of the need for welding of ferrules or other support components. The sub-miniature medical implants having the robust feedthrough of the present invention integrate the feedthrough wires, insulators, and sealing within a radially extending flange that is part of the end wall of the motor enclosure. This permits the largest feedthrough wire and thickest insulator to be built into the limited available space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/291,682filed Nov. 13, 2008, which is incorporated herein by reference in itsentirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under the Pumps forKids, Infants, and Neonate (PumpKIN) Pre-clinical Program, Grant No.HHSN268201000013C, awarded by National Institutes of Health (NIH). Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

Implantable medical devices that utilize electro-mechanical actuatorsmay be used for applications such as blood pumps, mechanically actuatedvalves, or artificial muscle. Electric motors (Jarvik, IntraventricularArtificial Hearts and Methods of Their Surgical Implantation and Use,U.S. Pat. No. 4,994,078), solenoids (Peters, Heart Assist Devices,Systems and Methods, U.S. Pat. No. 7,357,771) or linear actuators(Goldowski, Linear Pump, U.S. Pat. No. 5,924,975) that are used to powerthese devices utilize metals such as copper or iron, which are verysusceptible to corrosion if exposed to body fluids. Encapsulation,coating, potting, and similar methods that cover the metals with polymerbarrier layers may be used for short term implantation in the body, suchas days or weeks. But for electromechanical devices that must functionfor many years, complete exclusion of body fluids by use of hermeticallysealed enclosures is required. For decades pacemakers have utilizedwelded titanium cases to isolate batteries and electronics components,and have brought electrical conductors through the walls of these casesusing hermetic feedthroughs having metal to ceramic seals. Examplesinclude Kraska, Hermetic Electrical Feedthrough Assembly, U.S. Pat. No.4,678,868, and Sawchuk, Protective Feedthrough, U.S. Pat. No. 5,759,197.Many feedthroughs for heart devices and others electronic implants suchas cochlear implants or neuro-stimulators have been disclosed in theprior art including designs with multiple contacts such as Taylor,Implantable Medical Device with Multi-Pin Feedthrough, U.S. Pat. No.5,866,851, or Kuzma, Cochlear Prosthesis Package Connector, U.S. Pat.No. 4,516,820. This has been accomplished using materials such astitanium supports, aluminum oxide insulators, platinium-irridiumconductors and pure gold brazing to form a seal between the conductorsand the insulators, and between the insulators and the titanium supportor other methods such as glass to metal feedthroughs, (Spillman, Glassto Metal Seal, U.S. Pat. No. 6,670,074)

All of these feedthroughs are relatively small components, but in mostapplications the smallest and most compact geometries are not essential.For example, Wampler shows a multi-pin feedthrough in U.S PatentApplication No. 20070231135, entitled Rotary Blood Pump. This deviceuses three individual feedthroughs located in a recess of a wall of thehousing, and is placed in a portion of the centrifugal pump housing nearthe diffuser, where there is adequate space to weld a ferrule to thehousing. LaRose, in U.S. Patent Application No. 20070100196, discloses avery small axial flow blood pump, in which hermetic feedthroughs may beused for the electrical leads, but does not disclose a compactarrangement for the feedthroughs. Rather, LaRose states that thehermetically sealed motor stator enclosure may be welded to a tubularpump housing that passes through it, without providing a structure tocompactly provide feedthroughs for the electrical leads. But with verysmall diameter, generally cylindrical actuators, such as tiny axialblood pumps disclosed by Siess in U.S. Patent Application No.20040046466, entitled Miniature Motor, or by Jarvik in U.S. PatentApplication No. 20060195004, entitled, Minimally Invasive TransvalvularVentricular Assist Device, the available space to provide power leadsmay be as little as 2 mm or less. In Siess, no hermetic feedthrough isprovided because the device is for short-term application. The presentinvention provides an extremely compact hermetically sealed feedthroughfor tiny electromechanical actuators that integrate the feedthroughstructure with the device structure, without the use of a ferrule or theneed for welding the feedthrough onto an enclosure containing thestationary motor or solenoid coils.

OBJECTS OF THE INVENTION

1. It is an object of the invention to provide successful miniatureblood pumps to support the lives of infants and children.

2. It is an additional object of the invention to provide miniatureimplantable hermetically sealed electro-mechanical devices such as bloodpumps or linear actuators, having the smallest dimensions practical forthe necessary forces the devices must apply to tissues of the body.

3. It is a further object of the invention to provide the smallestpossible blood pump capable of corrosion free function when implantedfor many years.

4. Another object of the invention is to provide a practical andreliable generally cylindrical blood pump that is small enough to beimplanted with less invasive surgical techniques, such as roboticthorascopic procedures.

5. An additional object of the present invention is to integrate thestructure of hermetic feedthroughs into the motor housing of blood pumpswithout increasing the diameter of the devices that would be necessarywithout the use of any feedthroughs at all.

THE DRAWINGS

FIG. 1A is a longitudinal section of a prior art feedthrough that usesbrazed ceramic to metal components.

FIG. 1B is a longitudinal section of a prior art feedthrough that uses aglass to metal seal.

FIG. 2A is a partially cutaway drawing of a blood pump showing the motorhousing and other components without the motor stator and feedthroughwires.

FIG. 2B is a drawing of the motor stator of the blood pump partiallyshown in FIG. 2A, showing three motor lead wires emerging at the face ofthe stator, with each of the three wires wrapped tangentially.

FIG. 2C is a view of the inner sleeve of the pump showing a flange andfeedthrough wires passing through insulators supported by the flange toconnect the three motor leads to the electrical system and power cablesthat provide power and control of the motor.

FIG. 2D is a partially cutaway view of the motor stator (shown partiallycrosshatched) assembled within a compartment formed between the sleeveand housing components, and also showing the motor leads connected tothe feedthrough wires.

FIG. 3 (includes FIGS. 3A, 3B, and 3C) is a longitudinal section of ablood pump showing the connection of the motor leads and feedthroughwires and the positions of the welds that seal the motor stator withinthe housing. The magnified view of the feedthrough portion of the bloodpump, (FIG. 3A) shows the positions of the wire welds both within thehermetically sealed motor compartment and outside it. FIG. 3B is givento indicate the portion of the Pump magnified in FIG. 3A. FIG. 3C is alarger drawing similar to FIG. 3B, included to make the detail moreclearly apparent.

FIG. 4A is a view of the motor stator showing one lead wire, onefeedthrough insulator, and an elongated power cable that exits the pumphousing: this illustrates the electrical connections of the wires.

FIG. 4B is a partially sectioned cutoff view of the pump housing,sleeve, flange, and feedthrough components showing an arrangement oftangentially wrapped wires both inside the hermetically sealed motorcompartment, and on the other side of the flange.

SPECIFIC DESCRIPTION OF THE INVENTION

The present invention is adapted to provide a very compact hermeticallysealed implantable medical actuator able to be significantlyminiaturized. This is accomplished using metal to ceramic brazing orglass to metal types of seals and insulators or similar solid bondedcomponents. FIG. 1A shows an example from the prior art of a ceramic tometal feedthrough that uses a wire 2, brazed into a ceramic insulator 4,with a brazing material such as pure gold 6, 8. The ceramic insulator 4is in turn brazed into a metal ferrule with a flange 10 that can bewelded to the wall of a medical implant such as a pacemaker. FIG. 1Bshows a similar feedthrough element, having a wire 12 that is sealed toand insulated from a metal cylinder 14, by fused glass.

In the case of a very small medically implantable actuator there isoften a need to maintain the overall diameter of the device as small aspossible, for example, in case it is to be inserted into a smalldiameter blood vessel. There is a limit to how small the wires, ceramicinsulators, and components such as ferrules can be made, and space isinevitably lost if a feedthrough sub-assembly needs to be welded ontothe wall of a small diameter motor housing. The preferred embodiment ofthis invention uses a two piece motor housing having a thin walledsleeve 16, best seen in FIG. 2C, that passes through the center of amotor stator 18, shown by itself in FIG. 2B, and best seen together withthe motor housing 20, in FIG. 3C. Circumferential welds hermeticallyjoin the sleeve to one end of the housing at 22, and also hermeticallyjoin the housing to the outer circumference of a flange 24 at weld 26,thus defining an interior motor stator cavity, 28, within which themotor stator 18 is contained. After assembly and welding of the housingcomponents, Flange 24 constitutes one end wall of the motor statorenclosure. Flange 24 is pierced by two or more holes, 29, 30 at thelocations where feedthrough wires pass across an end wall of the motorhousing. By utilizing hermetically sealed and insulated components thatare directly bonded to the flange rather than using a separate ferrule(which would need to be welded to the flange), great space efficiency isobtained. The largest diameter feedthrough wires and thickest ceramic orglass insulators that will fit through the wall of the flange within theradial extent of the motor housing end wall can be used; this providesimportant strength and durability to the assembly, as well as the bestelectrical properties (low resistance conductor wire, and highresistance insulator) provided that optimal materials are selected.

An embodiment of a miniaturized implantable blood pump for use withinfants and children or for implantation in adults by less invasiveendoscopic procedures shown in FIG. 3C incorporates the presentinvention to permit use of the thinnest motor stator and thus minimizethe diameter of the pump. As shown in FIG. 4B, the lead wires 32, 34,36, may be arranged tangential to the long axis of the pump as shown orthey may be arranged to exit the pump substantially in parallel with thelong axis of the pump.

For any generally cylindrical rotary or linear motor stator, such as theone shown in FIG. 4A, the outside diameter 38 minus the bore diameter 40divided by two, represents the thickness of the motor stator components42 shown as the distance of the cross-hatched motor components betweenthe arrows in FIG. 3C.

In order to provide the largest diameter feedthrough wires andinsulators, most of this thickness must be utilized. Therefore, thediameter of the insulator 44 will typically be >50% of the motor statorthickness. Referring to FIG. 3A, hole 29 (shown elongated because it isnot formed perpendicular to flange 24, FIG. 3C) accommodates insulator44 through which a feedthrough wire 76 passes. The insulator has awidened end 48, that prevents it from passing all the way through hole29 in the flange, when the components are supported in the furnace inthe proper orientation during brazing (with the widened end up). In themanufacturing process, the wire may be brazed to insulator first andthen the insulator containing the brazed wire may be brazed into theflange. Typically, for a three phase motor, brazing three feedthroughwires and insulators to the flange may be done at the same time, usingbrazing locations similar to that shown in FIG. 1A. Typical materialsthat may be used include TiAl6V4 alloy for the pump housing having theflange, alumina for the insulator, platinum-iridium alloy wire for theelectrical conductor wire and pure gold for the brazing. The process maybe carried out in inert gas at approximately 2,000° F. Alternatively,the feedthrough wires may be affixed across the holes in flange 24 usingglass to metal bonding technology such as illustrated in FIG. 1B. Ifthis is done special fixturing may be used to hold the wires centered inthe holes in said flange without contacting it when the glassyinsulating material melts and fuses with the wire and the housingflange.

The blood pump incorporating the present invention, shown in FIG. 3C,includes the motor housing 20, housing sleeve component 16, which ismade integral with the flange 24. This sleeve component also includes asecond flange 50 and thus a groove 52 exists between the two flanges.This groove contains the feedthrough wires as they emerge from the motorcompartment 28, through the insulators. The external lead wires, thatconduct electric power to the motor from the battery or wall powersource, are electrically connected to the feedthrough wires withingroove 52, by usual methods such as welding, soldering or crimping.After the wires are attached and insulated, the groove containing themmay be encapsulated or potted with a durable insulating material such asepoxy in the manner that some pacemaker headers encapsulate feedthroughwires in epoxy. A cover, 54, which may be formed as two pieces, may beprovided to further protect the wires, and conduit 56 per FIG. 4B,designed to provide support for exit of the wires and attachment of astrain relief (not shown) may be formed integral with the cover.

Reviewing the structures shown in FIG. 3C described above, we havedisclosed an elongated, generally cylindrical motor enclosure whichconfines the motor within a hermetically sealed cavity when twocircumferential welds are made. The enclosure includes a flange with twoor more feedthroughs located on one end, or if required, on both ends.

Within the center of the motor bore the motor rotor 58, which carriesthe impeller 60 of a hydrodynamic pump, such as a mixed flow pump or anaxial flow pump, is supported for rotation by bearings, schematicallyillustrated at 62, 64. These may be blood immersed bearings, supportedby posts (not shown) extending inward from the motor housing assembly,or the rotor may be supported magnetically, or by a combination ofmagnetic and hydrodynamic forces, or by mechanical bearing members atthe tips of the pumping blades, etc. Any type of rotor bearings may beused. When power is appropriately applied to the various motor windingswithin the motor stator, magnetic forces are applied to the rotor magnet66, causing it to turn.

FIG. 2B-FIG. 2D illustrates the assembly of the blood pump motor intothe housing and the connections of the feedthrough wires to the motorwires and the external lead wires. In the case of a three phasebrushless DC motor only three wires are necessary. To best match theposition of three equally spaced feedthroughs, the motor wires 68, 70,72 exit the end of the motor stator at 120° angular separation and maybe wrapped in a generally tangential position as shown in FIG. 2B. Asbest seen in FIG. 2C the motor housing sleeve 16 has flange 24, withthree feedthroughs already formed, after removal from the furnace.Feedthrough wires 74, 76 and 78 are spaced 120° apart and can berotationally lined up with the motor wires. Each of the feedthroughwires has one end on the side of flange 24 that will be inside the motorenclosure 28 per FIG. 3C and one end on the other side of the flange.This is clearly seen for wire 76, that has one end 76 a inside the motorenclosure and the other end 76 b, outside the motor enclosure.

Referring to FIG. 2B-D it can be seen that the motor stator may beplaced over the sleeve, the motor wires may be connected to thefeedthrough wires and insulated, such as by welding as illustrated inFIG. 3A at 80, and then covering them with shrink fit tubing, and thenthe motor housing can be placed over the motor stator andcircumferentially welded together at positions 22 and 26 per FIG. 3C, aspreviously described.

FIGS. 4A and 4B most clearly show the feedthrough structures. FIG. 4A,which omits the motor enclosure sleeve, flange, and housing for clarity,shows the motor stator 38, one motor wire 72 and one feedthrough wire 76a welded to it at weld 80. The feedthrough wire passes through thecenter of one insulator 44 and they are brazed or otherwise hermeticallysealed together. The other part of this feedthrough 76 b is welded toone of the external motor leads, 32 at weld 82. FIG. 4B, includes themotor stator 18, sleeve 16, flange 24, motor housing 20, and wire coverwith conduit 56. The arrangement in which three motor wires areconnected to three feedthrough wires within the motor enclosure, and arein turn connected to three external motor leads within the groove formedbetween flange 24 and flange 50 is clearly apparent, although not all ofeach of the three feedthroughs and sets of wires is visible in thecut-away view.

It is also apparent to one skilled in the art that an embodiment of thepresent invention could be constructed in which the feedthroughs weremounted to a flange (or end wall) extending inwardly from the outer wallof the motor housing, rather than to a flange extending outwardly from asleeve as shown in the drawings. This additional configuration wouldmake connection of the motor wires to the feedthrough wires moredifficult, since the connection would need to be made inside the bore,but nonetheless, this could be accomplished and the resulting devicewould function properly.

Thus it is clear that the invention disclosed provides thin walledelectromechanical actuators for medical implants that incorporate aneffective space efficient integrated hermetic feedthrough. One type ofdevice disclosed is a highly miniaturized small diameter implantableblood pump.

The information disclosed in the description of the present invention isintended to be representative of the principles I have described. Itwill thus be seen that the objects of the invention set forth above andthose made apparent from the preceding description are efficientlyobtained and that certain changes may be made in the above articles andconstructions without departing from the scope of the invention. It isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative but notin a limiting sense. It is also understood that the following claims areintended to cover all of the generic and specific features of theinvention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to fall therebetween.

I claim:
 1. An implantable blood pump comprising; a. A slot-lessbrushless DC motor having a motor stator enclosed in a weldedhermetically sealed housing, b. A cylindrical bore through said housingwithin which a hydrodynamic pump rotor and impeller rotate on bearings,c. Three electric feedthroughs adapted to conduct electric power toterminations of said motor stator, circumferentially spaced apart fromone another at locations on one end of said housing, individuallyhermetically sealed, insulated, and formed integral with one end wall ofsaid housing, and d. the three hermetically sealed feedthroughs areenclosed within the housing.
 2. The blood pump of claim 1 having acircumferential groove outside and adjacent to one end of thehermetically sealed housing within which groove connections of motorpower leads to the electric feedthroughs may be made and encapsulated inan insulating material such as epoxy.
 3. A miniaturized implantablemedical device having a hermetically sealed corrosion resistantenclosure to contain the stator of an electro-magnetic actuator,comprising: a. a first generally cylindrical housing member having anouter generally tubular wall adapted to receive said motor stator withinsaid tubular wall, and a washer shaped end wall confining the motorstator on one end, b. A second generally cylindrical housing memberhaving a thin-walled sleeve adapted to fit through a bore of said motorstator and contact the hole within the washer shaped end wall of saidfirst housing member around its entire circumference, c. Said secondhousing member including a flange extending outwardly from said sleeveto enclose said motor stator and make circumferential contact with saidhousing, said flange having two or more hermetic feedthroughs, comprisedof wires passing through the flange, insulated by suitable materialhermetically bonded to the inside of holes passing through the flangeand also hermetically bonded to wires passing through holes in theinsulating material, d. Said first and second housing members weldedcircumferentially at each end to hermetically seal the motor statortherewithin, and e. Said two or more hermetic feedthroughs and saidwires passing through the flange are enclosed within the outer tubularwall.
 4. The feedthrough of claim 3 in which the medical device is animplantable rotary blood pump.
 5. The feedthrough of claim 3 in whicheach electric wire passes through a separate hole in said end wallwithin which it is sealed and insulated by a surrounding glass orceramic ring, and the diameter of said hole in the flange is greaterthan one half of the radial dimension of the motor stator containedwithin said enclosure.
 6. The feedthrough of claim 3 in which saidhermetically sealed enclosure contains a slot-less brushless DC motorstator.
 7. The feedthrough of claim 3 in which three electrical wiresare located around the circumference of the end wall at approximately90-180 degrees of separation, and the motor stator of theelectro-magnetic actuator includes three phase brushless DC motorwinding with terminations spaced circumferentially at positions alignedwith the wires.
 8. A hermetically sealed corrosion resistant enclosureto contain the stator of a miniaturized implantable medical devicecomprising: a. a first generally cylindrical housing member having anouter generally tubular wall adapted to receive said motor stator withinsaid tubular wall, and a washer shaped end wall confining the motorstator on one end, b. A second generally cylindrical housing memberhaving a thin-walled sleeve adapted to fit through a bore of said motorstator and contact the hole within the washer shaped end wall of saidfirst housing member around its entire circumference, c. Said secondhousing member including a flange extending outwardly from said sleeveto enclose said motor stator and make circumferential contact with saidhousing, d. said washer shaped end wall of said first housing memberhaving two or more hermetic feedthroughs, comprised of wires passingthrough the end wall, insulated by suitable material hermetically bondedto the inside of holes passing through the end wall and alsohermetically bonded to wires passing through holes in the insulatingmaterial, e. Said first and second housing members weldedcircumferentially at each end to hermetically seal the motor statortherewithin, and e. Said two or more hermetic feedthroughs and saidwires passing through the end wall are enclosed within the outer tubularwall.
 9. The feedthrough of claim 8 in which the medical device is animplantable rotary blood pump.
 10. The feedthrough of claim 8 in whicheach electric wire passes through a separate hole in said end wallwithin which it is sealed and insulated by a surrounding glass orceramic ring, and the diameter of said hole in the flange is greaterthan one half of the radial dimension of the motor stator containedwithin said enclosure.
 11. The feedthrough of claim 8 in which saidhermetically sealed enclosure contains a slot less brushless DC motorstator.
 12. The feedthrough of claim 8 in which three electrical wiresare located around the circumference of the end wall at approximately90-180 degrees of separation, and the motor stator of theelectro-magnetic actuator includes three phase brushless DC motorwinding with terminations spaced circumferentially at positions alignedwith the feedthrough wires.